The present invention relates to a Ski with Roughened Sliding Surface, particularly a cross-country ski, which has a polyethylene bottom layer with a roughened sliding surface.
Skis of the above-mentioned general type are known in the art. A known ski has a roughening on the sliding surface of the polyethylene bottom layer, which makes easier climbing of the ski and only insignificantly influences the sliding of the same. The roughening is composed of small projections which have a thickness substantially corresponding to 10.sup.-1 and their portions which are spaced from the ski are inclined toward the rear end of the latter. The above-mentioned thickness is the distance between the soles of the valleys between the individual projections of the roughening, and the distance between the peaks of the projections from the above-mentioned soles. In view of the fact that in practice the roughening has certain non-uniformities, the level of the soles and the level of the peaks are calculated as mean values. The expression that the projections with their portions remote from the ski are inclined toward the ski rear end also includes such a situation when some projections do not have such an inclination, as soon as the number of the projections which do not have the inclination is insignificantly small as considered with the number of the projections which do have the inclination. Order of values here means the order of value corresponding to the ten power; and the limit of the order of magnitude relative to the next greater one and the next smaller one is performed exponentially, for example the order of value 10.sup.x includes the region from 10.sup.(x-1/2) to 10.sup.(x+1/2). This region can also be easily defined in that it extends between one-third of the indicated ten power to substantially three times the same. In the known ski, the roughening is composed of grooves which extend transverse to the direction of elongation of the ski. The roughening has respectively a structure which is formed by a plurality of neighboring ribs and valleys alternating with and merging into one another, having more or less sharp edges, and extending transverse to the direction of elongation of the ski. In the region of the tips, the ribs are fuzzed and inclined toward the ski rear end under the action of a subsequent treatment. The above inclination to the rear end of the ski is insignificant in the known skis. Since the roughened region of the known ski is provided only under the binding region and extends in direction of elongation of the ski only over a portion between one-third and one-fifth of the same, such skis, because of the obtained flake profile, are advantageous as compared with other skis since they provide for help in pushing off, and also improve the safety against rearward sliding during climbing at least in condition of icy runways. The increased friction resistance in the central region of the ski is not very disturbing, inasmuch as during sliding the weight of the skier is not completely applied to the individual ski. During pushing off and climbing in the respective phase, the weight of the skier is applied fully to the ski, and the ski is pressed with its central upwardly curved part downwardly into the snow, so that the transverse profiling engages stronger with the latter.
Another ski has a bottom layer of synthetic plastic material, such as polyester, epoxide-polyurethane resin or phenol resin, and a plush-like textile fabric is embedded in the layer so that the fibers of the fabric extend at least to the sliding surface of the bottom layer. The extending fabric fibers can have in the end regions a small curvature toward the rear ski end. The extension of the tips of the fibers outwardly beyond the sliding surface must be obtained by grinding of the sliding surface of the bottom layer. Thereby the textile fibers can extend outwardly beyond the sliding surface of the bottom layer by a distance of up to 1 mm. Such a construction is rarely utilized in practice. During grinding of the sliding surface of the synthetic plastic layer, the threads of the embedded fabric do not remain standing, but instead they are ground off. When a fabric of a considerable hard material is selected for the bottom layer, the above-mentioned extension of the fiber ends outwardly of the sliding face of the bottom layer can be attained by grinding. However, the hard fibers possess low sliding characteristics and hinder the sliding of the ski forwardly in the event when their extension is sufficient to help in pushing off or climbing. Further, ice tends to set on such bottom layers in the hard region very easily. Moreover, the embedding of the fabric having a nap in a very thin synthetic plastic layer serving as a ski bottom encounters considerable technical difficulties, particularly when it is necessary to provide that the threads of the nap at least with their tips have a uniform inclination in a predetermined direction. Thereby, this solution is not practically utilized because of the above-mentioned considerations.